Method and system for engine cold-start

ABSTRACT

Methods and systems are provided for adjusting engine cranking speed, fueling, and spark initiation to increase fuel vaporization during cold-start conditions. In one example, a method may include, during engine cold-start, cranking the engine at a lower speed relative to a nominal cranking speed while injecting fuel and disabling spark for a number of engine cycles, and after the completion of the number of engine cycle increasing the cranking speed and initiating spark.

FIELD

The present description relates generally to methods and systems forcranking an engine during a cold-start condition.

BACKGROUND/SUMMARY

Alternate fuels have been developed to mitigate the rising prices ofconventional fuels, to reduce dependence on imported fuels, and forreducing production of pollutants, such as CO₂. For example, alcohol andalcohol-based fuel blends have been recognized as attractive alternativefuels, in particular for automotive applications. However, alcohol andalcohol-based fuels are less volatile than diesel, and as such may notevaporate effectively during engine cranking at cold-start conditions.Incomplete vaporization of the alcohol and alcohol-based fuels mayreduce fuel economy and degrade emissions.

Various approaches are provided for increasing fuel vaporization duringcold-start. In one example, as shown by Samejima in JP 2009002314A, anengine cranking speed is adjusted. In particular, a higher enginecranking speed is applied when the alcohol concentration of the injectedfuel is high and the ambient temperature is low. In another exampleapproach shown by Kuroki in JP 2008232007, a starter motor speed isincreased when there is an issue with fuel vaporization. In a furtherexample, Ulrey et al. in U.S. Pat. No. 9,346,451 disclose a method ofcranking the engine unfueled at a lower than normal speed such that theheat generated in the compression stroke of a cylinder may betransferred to cylinder walls, thereby expediting engine warm-up.

However, the inventors herein have recognized potential issues with suchapproaches. In the approaches shown by Samejima and Kuroki, the starterspeed is increased to rapidly reduce the intake manifold pressure sincethe lower pressure assists in fuel vaporization. However, the rapidreduction in manifold pressure via the increasing of the starter speedalso reduces the time available for vaporizing the fuel. Consequently,it may be difficult to optimize the starter speed for both the manifoldpressure and the fuel alcohol content. Also, increased cranking speedduring engine start may result in engine flares. An optimal amount ofvaporized fuel may be desired to maintain combustion stability.Incomplete fuel vaporization may further lead to cylinder misfiringevents. In the approach shown by Ulrey et al., since the engine iscranked unfueled at a lower cranking speed, once fueling is initiated,fuel blends with a higher alcohol content may not get sufficient timefor vaporization before combustion is initiated.

In one example, the issues described above may be addressed by an enginemethod comprising: for a number of engine cycles since a first enginecycle of an engine cold-start, cranking the engine via a starter motorwith cranking speed decreased relative to a nominal cranking speed whileinjecting fuel and disabling spark; and after the number of enginecycles with injected fuel compressed and expanded, increasing thecranking speed to the nominal cranking speed and initiating spark. Inthis way, by cranking the engine via a starter motor at a lower crankingspeed while fueling the engine without spark until a number of enginecycles are completed, sufficient time may be provided to vaporize thefuel and provide a homogeneous air-fuel mixture. By raising the crankingspeed and resuming spark after the number of engine cycles have elapsed,the intake manifold pressure may be lowered and cylinder combustion canbe performed with a higher degree of fuel vaporized before combustion isinitiated.

As one example, during cold-start conditions, a starter motor may beactuated to crank the engine. The cranking speed may be lowered relativeto a nominal cranking speed while fuel is injected into the engine withspark disabled for a number of engine cycles. The number of enginecycles and the cranking speed may be selected based on the alcoholcontent of the injected fuel and the ambient temperature so as to enablea larger portion of the fuel to be vaporized by the time spark isenabled. As an example, the cranking speed may be lowered to 150 rpm,and the engine may be fueled with no spark for two complete enginecycles (e.g., the first two engine cycles since engine start isinitiated). On the subsequent engine cycle (e.g., the third engine cyclesince the engine is started), the cranking speed may be raised, forexample to 250 rpm, and spark may be resumed. To further improve fuelvaporization, fuel injection timing may be adjusted to extend up tillthe spark event. For example, an end of fuel injection timing may beshifted from bottom dead center (BDC) of the intake stroke to top deadcenter (TDC) of compression stroke.

In this way, by lowering cranking speed to below the nominal speed, alarger time window is provided for fuel vaporization. Also, by using alower engine cranking speed, engine speed flares may be reduced. Bycontinuing fuel injection until spark, a higher amount of fuel may beinjected which may result in an increase in the amount of vaporized fuelavailable for combustion. The technical effect of deactivating sparkuntil a defined number of fueled engine cranking cycles have elapsed isthat each cylinder may be conditioned with vaporized fuel and uponactivating spark after accumulation of an optimal amount ofpre-vaporized fuel, combustion stability may be improved. By improvingcombustion stability, misfire event occurrence and unburned hydrocarbonemissions during engine starts may be reduced. By increasing thecranking speed after the number of engine cycles have elapsed, thedesired intake manifold pressure may be attained, facilitatingcombustion. By adjusting the cranking speed, fuel injection profile, andthe number of non-firing cycles based on the alcohol content of thefuel, vaporization of any variety of alcohol fuel may be optimized.Overall, by increasing the degree of fuel alcohol vaporization, engineperformance, fuel economy, and emissions quality may be increased.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example embodiment of an engine system including astarter motor.

FIG. 2 shows a flow chart illustrating an example method that may beimplemented for increasing fuel vaporization during cold-startconditions.

FIG. 3 shows an example change in air charge temperature and fuelboiling point with change in cranking speed.

FIG. 4 shows an example map of piston positions with respect to anengine position, for a given engine cylinder, during cranking.

FIG. 5 shows an example map of injection timing, spark timing, andcranking speed for a given engine cylinder, during cranking.

FIG. 6A shows a first statistical example of first firing eventcombustion stability at a first cranking speed.

FIG. 6B shows a second statistical example of first firing eventcombustion stability at a second cranking speed.

FIG. 6C shows a third statistical example of first firing eventcombustion stability at a third cranking speed.

DETAILED DESCRIPTION

The following description relates to systems and methods for increasingfuel vaporization during engine cranking under cold-start condition. Anexample embodiment of an engine system comprising a starter motor, anignition system, and a fuel system is shown at FIG. 1. An enginecontroller may be configured to perform control routines, such as theexample routine of FIG. 2, to adjust cranking speed, fuel injection, andspark initiation to increase fuel vaporization during cold-startconditions. Changes in air charge temperature and fuel boiling point dueto change in cranking speed under cold-start conditions is shown in FIG.3. FIGS. 4 and 5 show adjustments to fueling schedule, spark timing, andcranking speed, during cold-start conditions. Adjustments to each of thefueling schedule, the spark timing, and the cranking speed may be basedon the alcohol (e.g., ethanol) content of the fuel to improve combustionstability and reduce occurrence of engine start misfires. FIGS. 6A-6Cshow statistical examples of first firing event combustion stability andmisfire occurrence at different cranking speeds.

FIG. 1 is a schematic diagram showing one cylinder of multi-cylinderengine 10, which may be included in a propulsion system of anautomobile. Engine 10 may be controlled at least partially by a controlsystem including controller 12 and by input from a vehicle operator 130via an input device 132. In this example, input device 132 includes anaccelerator pedal and a pedal position sensor 134 for generating aproportional pedal position signal PP. Combustion chamber (i.e.cylinder) 30 of engine 10 may include combustion chamber walls 136 withpiston 138 positioned therein. Piston 138 may be coupled to crankshaft140 so that reciprocating motion of the piston is translated intorotational motion of the crankshaft. Crankshaft 140 may be coupled to atleast one drive wheel of a vehicle via an intermediate transmissionsystem. Further, a starter motor 190 may be coupled to crankshaft 140via a flywheel to enable a starting operation (cranking) of engine 10.

Cylinder 30 can receive intake air via a series of intake air passages142, 144, and 146. Intake air passage 146 can communicate with othercylinders of engine 10 in addition to cylinder 30. In some embodiments,one or more of the intake passages may include a boosting device such asa turbocharger or a supercharger. For example, FIG. 1 shows engine 10configured with a turbocharger including a compressor 174 arrangedbetween intake passages 142 and 144, and an exhaust turbine 176 arrangedalong exhaust passage 148. Compressor 174 may be at least partiallypowered by exhaust turbine 176 via a shaft 180 where the boosting deviceis configured as a turbocharger. However, in other examples, such aswhere engine 10 is provided with a supercharger, exhaust turbine 176 maybe optionally omitted, where compressor 174 may be powered by mechanicalinput from a motor or the engine. A throttle 20 including a throttleplate 164 may be provided along an intake passage of the engine forvarying the flow rate and/or pressure of intake air provided to theengine cylinders. For example, throttle 20 may be disposed downstream ofcompressor 174 as shown in FIG. 1, or alternatively may be providedupstream of compressor 174.

Exhaust passage 148 can receive exhaust gases from other cylinders ofengine 10 in addition to cylinder 30. In one example, exhaust passage148 may receive exhaust from all the cylinders of engine 10. However, insome embodiments, as elaborated at FIG. 2, the exhaust from one or morecylinders may be routed to a first exhaust passage, while the exhaustfrom one or more other (remaining) cylinders may be routed to a second,different exhaust passage, the distinct exhaust passages then convergingfurther downstream, at or beyond an exhaust emission control device.Exhaust gas sensor 128 is shown coupled to exhaust passage 148 upstreamof emission control device 178. Sensor 128 may be selected from amongvarious suitable sensors for providing an indication of exhaust gasair/fuel ratio such as a linear oxygen sensor or UEGO (universal orwide-range exhaust gas oxygen), a two-state oxygen sensor or EGO (asdepicted), a HEGO (heated EGO), a NOx, HC, or CO sensor, for example.Emission control device 178 may be a three way catalyst (TWC), NOx trap,various other emission control devices, or combinations thereof.

Exhaust temperature may be estimated by one or more temperature sensors(not shown) located in exhaust passage 148. Alternatively, exhausttemperature may be inferred based on engine operating conditions such asspeed, load, air-fuel ratio (AFR), spark retard, etc. Further, exhausttemperature may be computed by one or more exhaust gas sensors 128. Itmay be appreciated that the exhaust gas temperature may alternatively beestimated by any combination of temperature estimation methods listedherein.

Each cylinder of engine 10 may include one or more intake valves and oneor more exhaust valves. For example, cylinder 30 is shown including atleast one intake poppet valve 150 and at least one exhaust poppet valve156 located at an upper region of cylinder 30. In some embodiments, eachcylinder of engine 10, including cylinder 30, may include at least twointake poppet valves and at least two exhaust poppet valves located atan upper region of the cylinder.

Intake valve 150 may be controlled by controller 12 by cam actuation viacam actuation system 151. Similarly, exhaust valve 156 may be controlledby controller 12 via cam actuation system 153. Cam actuation systems 151and 153 may each include one or more cams and may utilize one or more ofcam profile switching (CPS), variable cam timing (VCT), variable valvetiming (VVT) and/or variable valve lift (VVL) systems that may beoperated by controller 12 to vary valve operation. The position ofintake valve 150 and exhaust valve 156 may be determined by valveposition sensors 155 and 157, respectively. In alternative embodiments,the intake and/or exhaust valve may be controlled by electric valveactuation. For example, cylinder 30 may alternatively include an intakevalve controlled via electric valve actuation and an exhaust valvecontrolled via cam actuation including CPS and/or VCT systems. In stillother embodiments, the intake and exhaust valves may be controlled by acommon valve actuator or actuation system, or a variable valve timingactuator or actuation system.

Engine 10 may further include an exhaust gas recirculation (EGR) systemto route a portion of exhaust gas from exhaust passage 148 to intakemanifold 144. FIG. 1 shows a low pressure EGR (LP-EGR) system, but analternative embodiment may include only a high pressure EGR (HP-EGR)system, or a combination of both LP-EGR and HP-EGR systems. The LP-EGRis routed through LP-EGR passage 149 from downstream of turbine 176 toupstream of compressor 174. The amount of LP-EGR provided to intakemanifold 144 may be varied by controller 12 via LP-EGR valve 152. TheLP-EGR system may include LP-EGR cooler 158 to reject heat from the EGRgases to engine coolant, for example. For example, one or more sensors159 may be positioned within LP-EGR passage 149 to provide an indicationof one or more of a pressure, temperature, and air-fuel ratio of exhaustgas recirculated through the LP-EGR passage. When included, the HP-EGRsystem may route HP-EGR through a dedicated HP-EGR passage (not shown)from upstream of turbine 176 to downstream of compressor 174 (andupstream of intake throttle 20), via an HP-EGR cooler. The amount ofHP-EGR provided to intake manifold 144 may be varied by controller 12via an HP-EGR valve (not shown).

Each cylinder of engine 10 may include a spark plug 192 for initiatingcombustion. Ignition system 192 can provide an ignition spark tocombustion chamber 30 via spark plug 192 in response to spark advancesignal SA from controller 12, under select operating modes. Inparticular, in response to the spark signal from the controller,ignition system 192 may apply a high-voltage bias across spark plug 192to enable ionization sensing. The high-voltage bias may be appliedacross the spark gap and may be applied prior to ignition coil dwell.

In some embodiments, each cylinder of engine 10 may be configured withone or more fuel injectors for providing fuel thereto. As a non-limitingexample, cylinder 30 is shown including one fuel injector 166. Fuelinjector 166 is shown coupled directly to cylinder 30 for injecting fueldirectly therein in proportion to the pulse width of signal FPW receivedfrom controller 12 via electronic driver 168. In this manner, fuelinjector 166 provides what is known as direct injection (hereafter alsoreferred to as “DI”) of fuel into combustion cylinder 30. While FIG. 1shows injector 166 as a side injector, it may also be located overheadof the piston, such as near the position of spark plug 192. Such aposition may improve mixing and combustion when operating the enginewith an alcohol-based fuel due to the lower volatility of somealcohol-based fuels. Alternatively, the injector may be located overheadand near the intake valve to improve mixing. It will be appreciatedthat, in an alternate embodiment, injector 166 may be a port injectorproviding fuel into the intake port upstream of cylinder 30.

It will be appreciated that in still further embodiments, the engine maybe operated by injecting a variable fuel blend or knock/pre-ignitionsuppressing fluid via two injectors (a direct injector 166 and a portinjector) and varying a relative amount of injection from each injector.

Fuel may be delivered to fuel injector 166 via a high pressure fuelsystem 80, including fuel tanks, fuel pumps, and a fuel rail.Alternatively, fuel may be delivered by a single stage fuel pump atlower pressure, in which case the timing of the direct fuel injectionmay be more limited during the compression stroke than if a highpressure fuel system is used. Further, while not shown, the fuel tanksmay have a pressure transducer providing a signal to controller 12.

Fuel may be delivered by the injector(s) to the cylinder during a singleengine cycle of the cylinder. Further, the distribution and/or relativeamount of fuel delivered from the injector(s) may vary with operatingconditions. For example, the distribution may vary with a rate of changeof a cylinder aircharge, a nature of an abnormal cylinder combustionevent (such as, whether there is a cylinder misfire event, knock event,or pre-ignition event). Furthermore, for a single combustion event,multiple injections of the delivered fuel may be performed per cycle.The multiple injections may be performed during the compression stroke,intake stroke, or any appropriate combination thereof.

As described above, FIG. 1 shows only one cylinder of a multi-cylinderengine. As such each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector(s), spark plug, etc.

Fuel tanks in fuel system 80 may hold fuel or knock/pre-ignitionsuppressing fluids with different qualities, such as differentcompositions. These differences may include different alcohol content,different water content, different octane, different heat ofvaporizations, different fuel blends, and/or combinations thereof etc.In one example, fuels or knock/pre-ignition suppressing fluids withdifferent alcohol contents could include one fuel being gasoline and theother being ethanol or methanol. In another example, the engine may usegasoline as a first substance and an alcohol containing fuel blend suchas E10 (which is approximately 10% ethanol and 90% gasoline) or E100(which is approximately 100% ethanol) as a second substance. Otheralcohol containing fuels could be a mixture of alcohol and water, amixture of alcohol, water, and gasoline etc. In yet another example, oneof the fluids may include water while the other fluid is gasoline or analcohol blend. Additionally, the first and second fuels may also differin other fuel qualities such as a difference in temperature, viscosity,octane number, latent enthalpy of vaporization etc. The fuel alcohollevel may be estimated based on input from an alcohol level sensorcoupled to the fuel system 80.

Alcohol and alcohol-based fuel blends may have higher boiling points andas such may not evaporate effectively during engine cranking atcold-start conditions. Incomplete vaporization of such alcohol andalcohol-based fuel blends may reduce fuel economy and degrade emissions.In addition, the reduced fuel vaporization may compromise combustionstability and cause misfires during engine starts. As elaborated herein,an engine controller may improve fuel vaporization and enginestartability with alcohol fuels by reducing a cranking speed andadjusting a fuel and spark schedule for a defined number of enginecycles since a first engine cycle since an engine start.

In one example, during a first engine cold-start of an alcohol-fueledengine, the engine may be cranked via a starter motor 190 at a crankingspeed that is decreased relative to a nominal cranking speed with sparkenabled and cylinder fueling enabled during an intake stroke. During thefirst cold-start, fuel injection may be initiated after bottom deadcenter (BDC) of the intake stroke of an engine cycle and after intakevalve closing and terminated at bottom dead center (BDC) of the intakestroke. By cranking the engine at a lower cranking speed, the timeavailable for fuel vaporization (vaporization time) during which the aircharge temperature is higher than the boiling point of the fuel isprolonged.

In another example, during a second engine cold-start of thealcohol-fueled engine, the engine may be cranked via the starter motor190 at the decreased cranking speed with spark enabled and cylinderfueling extended from the intake stroke into the compression stroke. Inyet another example, during a third engine cold-start of thealcohol-fueled engine, the engine may be cranked via the starter motor190 at the decreased cranking speed with spark disabled and injectedfuel compressed and expanded for a number of engine cycles, and thenafter the completion of the number of engine cycles, spark may beinitiated. During each of the second and third cold-start, fuelinjection may be started after BDC of the intake stroke and ended at TDCof the compression stroke. By extending fueling into the compressionstroke, a higher volume of fuel may be injected and vaporized beforespark is initiated. The number of engine cycles over which spark isdisabled may be based on the alcohol content of the injected fuel andair charge temperature. The number of engine cycles may be increased asthe alcohol content increases and the air charge temperature decreases.This allows more alcohol fuel to vaporize during cold conditions. Thenumber of engine cycles may be decreased as the alcohol contentdecreases and the air charge temperature increases. Once the enginereaches the idling speed the starter motor 190 operation may bediscontinued.

During the first, second, and third cold-starts, there may be adifference in the alcohol content of the fuel injected and/or the aircharge temperature. As such, an alcohol content of fuel injected duringthe third cold-start may be higher than the alcohol content of fuelinjected during the second cold-start, and the alcohol content of fuelinjected during the second cold-start may be lower than the alcoholcontent of fuel injected during the first cold-start. Similarly, an aircharge temperature during the third cold-start may be lower than the aircharge temperature during the second cold-start, and the air chargetemperature during the second cold-start may be lower than the aircharge temperature during the first cold-start. Due to the higheralcohol content of fuel injected and/or lower air charge temperatureduring the third cold-start, in addition to lowering the cranking speedand extending the fueling (increasing fueling amount), spark may bedisabled for the number of engine cycles to facilitate increased fuelvaporization (before combustion) and combustion stability. Details ofthe method of adjusting engine cranking speed, fueling, and initiationof spark during cold-start conditions are discussed in relation to FIG.2.

Engine 10 may further include one or more knock sensors, accelerometers,vibrations sensors, or in-cylinder pressure sensors to sense engineblock vibrations, such as those related to knock or pre-ignition.Further, the accelerometers, vibrations sensors, in-cylinder pressuresensors, and a crankshaft acceleration sensor 120 may be used toindicate a cylinder misfire event, such as a cylinder misfire eventtriggered by incomplete fuel vaporization before spark.

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 106, input/output ports 108, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 110 in this particular example, random access memory 112,keep alive memory 114, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 122; engine coolant temperature (ECT)from temperature sensor 116 coupled to cooling sleeve 118; a profileignition pickup signal (PIP) from Hall effect sensor 120 (or other type)coupled to crankshaft 140; throttle position (TP) from a throttleposition sensor; absolute manifold pressure signal (MAP) from sensor124, manifold charge temperature (MCT) from temperature sensor 145;cylinder AFR from EGO sensor 128, abnormal combustion from a knocksensor and a crankshaft acceleration sensor; and fuel alcohol level froman alcohol level sensor coupled to the fuel system. Engine speed signal,RPM, may be generated by controller 12 from signal PIP. Manifoldpressure signal MAP from a manifold pressure sensor may be used toprovide an indication of vacuum, or pressure, in the intake manifold.Still other sensors such as cylinder pressure sensors, knock sensors,and/or pre-ignition sensors may be coupled to engine 10 (e.g., to a bodyof the engine) to help in the identification of abnormal combustionevents. The controller 12 receives signals from the various sensors ofFIG. 1 and employs the various actuators of FIG. 1 to adjust engineoperation based on the received signals an instructions stored on amemory of the controller. In one example, during an engine start, basedon input from one or more of engine coolant temperature sensor and amanifold charge temperature 145, the controller 12 may infer acold-start condition and actuate the starter motor 190 to crank theengine at a lower than nominal speed. During the cold-start condition,the controller 12 may also send a signal to the ignitions system 192 andto the fuel system 80 to suspend spark until the completion of a numberof engine cycles while maintaining fueling. Storage medium read-onlymemory 110 can be programmed with computer readable data representinginstructions executable by processor 106 for performing the methodsdescribed below as well as other variants that are anticipated but notspecifically listed.

In this way, the system of FIG. 1 provides for a vehicle systemcomprising: a starter motor; an engine including an intake manifold, aplurality of cylinders, and an exhaust manifold; an exhaust temperaturesensor coupled to the exhaust manifold; an air charge temperature sensorcoupled to the intake manifold; a crankshaft position sensor coupled toa crankshaft; a fuel system including one or more fuel injectors coupledto the plurality of cylinders; an ignition system including one or morespark plugs coupled to the plurality of cylinders; and a controller withcomputer readable instructions stored on non-transitory memory for: inresponse to an engine cold-start condition, actuating the starter motorto crank the engine at a lower than nominal cranking speed, actuatingthe fuel injectors to inject fuel from after a bottom dead center (BDC)of an intake stroke to TDC of a compression stroke, and deactivatingspark for a number of number of engine cycles after engine start; andafter completion of the number of engine cycles, actuating the startermotor to crank the engine at the nominal cranking speed, maintainingfueling from TDC of the intake stroke to TDC of the compression stroke,actuating the park plug to initiate spark at TDC of the compressionstroke until engine idling speed is reached.

FIG. 2 illustrates an example method 200 that may be implemented forincreasing fuel vaporization during engine start under cold-startconditions. Instructions for carrying out method 200 and the rest of themethods included herein may be executed by a controller based oninstructions stored on a memory of the controller and in conjunctionwith signals received from sensors of the engine system, such as thesensors described above with reference to FIG. 1. The controller mayemploy engine actuators of the engine system to adjust engine operation,according to the methods described below.

At 202, the routine includes estimating and/or measuring engineoperating conditions. Conditions assessed may include, for example,driver demand, engine temperature, engine load, engine speed, exhausttemperature, air charge temperature, ambient conditions includingambient temperature, pressure, and humidity, manifold pressure andtemperature, boost pressure, exhaust air/fuel ratio, etc. Also, thecontroller may determine the fuel octane or alcohol rating of the fuelto be injected into the cylinders as the engine is cranked. As anexample, an alcohol fuel blend may be used and the alcohol (e.g.ethanol) content of the fuel may be determined since the percentage ofalcohol in the fuel blend determines the boiling point of the fuel. Asexamples, E10 (10% Ethanol, 90% gasoline), E85 (85% Ethanol, 15%gasoline), E100 (100% Ethanol) may be used as fuel blends.Alternatively, pure gasoline (without any added alcohol) may be used inthe vehicle fuel system. The boiling point of the fuel may be determinedas a function of the alcohol content of the fuel. As gasoline andalcohol-based fuel blends are less volatile than diesel, the entirevolume of the injected fuel may not be vaporized during engine crankingat nominal speed during cold-start conditions. Fuel boiling point may befurther based on the octane content of the fuel. In one example, thefuel boiling point may be raised relative the boiling point of a fuelhaving a nominal octane rating (e.g., based on a gasoline fuel with noalcohol added) as the fuel octane content or alcohol content increases.All or part of the fuel may vaporize when the air charge temperature (orin-cylinder temperature) increases above the fuel boiling point. Thefuel may vaporize within the vaporization time window before spark whenin-cylinder (air charge) temperature is higher than the boiling point ofthe fuel.

At 204, the routine includes confirming an engine cold-start condition.An engine cold-start condition may be confirmed when the engine isstarted after a prolonged period of engine inactivity while the enginetemperature is lower than a threshold (such as below an exhaust catalystlight-off temperature), and while ambient temperatures are below athreshold.

If engine cold-start conditions are confirmed, at 206, the controllermay send a signal to an actuator coupled to the starter motor (such asstarter motor 190 in FIG. 1) to crank the engine using energy from thestarter motor. At 208, the cranking speed of the engine on the firstengine cycle since the engine start, and for a number of cyclesthereafter, may be lowered to below the nominal cranking speed of theengine. In one example, the nominal cranking speed may be 250 rpm andthe lowered cranking speed used during cold-start conditions may be 150rpm. Due to the lower cranking speed, the time between the pistonposition corresponding to the bottom dead center (BDC) and the top deadcenter (TDC) of the compression stroke may increase. Therefore, thevaporization time when the air charge temperature is higher than thefuel boiling point may increase, thereby increasing the time windowavailable for the fuel to vaporize before the time to spark at TDC (atthe end of compression stroke). Due to the longer vaporization timewindow, there may be an increase in the degree of fuel vaporizationbefore spark. The degree of lowering of the cranking speed relative tothe nominal speed may be adjusted based on each of the air chargetemperature and the fuel boiling point or fuel alcohol content. The fuelboiling point may be proportional to the fuel alcohol content, theboiling point increasing as the alcohol content increases. In oneexample, the degree of lowering of the cranking speed may be decreased(cranking speed moved closer to the nominal speed) as one or both of aircharge temperature increases and fuel alcohol content decreases. Inanother example, the degree of lowering may be increased (cranking speedmoved further below the nominal speed) as one or both of air chargetemperature decreases and fuel alcohol content increases. The degree oflowering of the cranking speed based on the fuel alcohol content mayoccur at a different rate than the degree of lowering of the crankingspeed based on the air charge temperature. In one example, the crankingspeed may be decreased by a larger amount responsive to a rise in thefuel alcohol content as compared to a drop in the air chargetemperature.

For example, the controller may determine a control signal to send tothe starter motor actuator, such as a signal corresponding to a desiredstarter motor speed, the signal determined based on each of the aircharge temperature and fuel alcohol content. The controller maydetermine the cranking speed through a determination that directly takesinto account each of a determined air charge temperature and a fuelalcohol content. The controller may alternatively determine the crankingspeed based on a calculation using a look-up table with the input beingeach of the air charge temperature and the fuel alcohol content and theoutput being desired cranking speed (starter motor speed) or desireddrop in cranking speed relative to a default/nominal cranking speed. Asanother example, the controller may make a logical determination (e.g.,regarding the cranking speed) based on logic rules that are a firstfunction of air charge temperature and a second, different function offuel alcohol content. The controller may then generate a control signalthat is sent to the starter motor actuator.

At 210, as the engine is being cranked at the lower than nominal speed,fueling may be initiated. During the engine cold-start, while the engineis being cranked, an engine controller may be configured to adjust aninjection profile of fuel delivered to the cylinder. During enginecranking at the nominal speed, the end of injection timing may be at thebottom dead center (BDC) of the intake stroke. As the cranking speed islowered from the nominal speed and an equal amount of fuel is injectedat an equal rate (as injected during cranking at nominal speed), theremay be a time gap between the end of injection timing and the BDC ofintake stroke. Fueling may be continued during this time gap and alsoduring the compression stroke. As such, the end of fuel injection timingmay be adjusted to coincide with spark at the top dead center (TDC) ofcompression stroke. As such, fueling may be initiated after bottom deadcenter (BDC) of the intake stroke of an engine cycle and after intakevalve closing such that heating of the intake charge has started due tocompression and terminated at TDC of the compression stroke.

By continuing to inject fuel up to the TDC of compression stroke, alarger amount of fuel may be injected and vaporized. Spark may bedisabled for a number of engine cycles while fueling is continued. Byinitiating spark after a number of engine cranking cycles, an amount ofpre-vaporized fuel may be available for combustion thereby improvingcombustion stability. Also, as the fuel is compressed and expanded overthe engine strokes without spark, a higher amount of fuel may vaporizeand the cylinder walls may be heated. The heat generated during thecylinder compression stroke may directly heat the cylinder walls,thereby improving stability of upcoming combustion events and emissionsquality. During the expansion stroke of the non-firing cycles, thevaporized fuel may be drawn into the cylinder, thereby reducing thepossibility of increased tail-pipe emissions caused by un-combusted fuelvapors.

At 212, the routine includes determining if the number of engine cyclesthat were fueled but not fired since the engine start (including a firstengine cycle since the engine start) is above a threshold number. Thethreshold number of non-firing engine cycles may be selected based oneach of the alcohol content of the injected fuel and the air chargetemperature so as to enable a larger portion of the fuel to be vaporizedby the time spark is enabled. As an example, the threshold number ofnon-firing cycles may be increased as at least one of the alcoholcontent of the fuel increases and the air charge temperature decreasesand the threshold number of non-firing cycles may be decreased as atleast one of the alcohol content of the fuel decreases and the aircharge temperature increases. As such, the number of cycles (when sparkis disabled and fueling enabled) based on the fuel alcohol content maybe different from the number of non-firing cycles based on the aircharge temperature. In one example, the number of non-firing cycles maybe increased by a responsive to a rise in the fuel alcohol content ascompared to a drop in the air charge temperature.

For example, the controller may determine a control signal to send tothe spark plug, such as a signal corresponding to a desired time toresume spark, the signal determined based on each of the air chargetemperature and fuel alcohol content. The controller may determine thetime of spark enablement through a determination that directly takesinto account each of a determined air charge temperature and a fuelalcohol content. The controller may alternatively determine the time ofspark enablement based on a calculation using a look-up table with theinput being each of the air charge temperature and the fuel alcoholcontent and the output being the desired time for resuming spark. Asanother example, the controller may make a logical determination (e.g.,regarding resuming spark) based on logic rules that are a first functionof air charge temperature and a second, different function of fuelalcohol content. The controller may then generate a control signal thatis sent to the spark plug actuator.

If it is determined that the number of non-firing cycles completed islower than the threshold number, at 214 cranking may be continued at thelower speed while continuing fueling (with fueling extended into thecompression stroke) and with spark maintained disabled.

If it is determined that a threshold number of non-firing cycles hasbeen completed since a first engine cycle of the engine start, at 216,spark may be enabled. For example, spark may be resumed at TDC of thecompression stroke. In one example, after completion of the number ofengine cycles, the engine may be cranked via the starter motor at ahigher cranking speed with fuel injection enabled and spark enabled. Thehigher cranking speed may be equal to or lower than the nominal crankingspeed that may be used for engine start during hot-start conditions. Byraising the cranking speed after the number of engine cycles have beencompleted, the intake manifold pressure may be lowered and cylindercombustion can be performed with a higher degree of fuel vaporizedbefore spark is initiated. In another example, after completion of thenumber of engine cycles, the engine may continue to be cranked via thestarter motor at the lower than nominal cranking speed with fuelinjection enabled and spark enabled.

At 218, fuel injection timing may be adjusted to continue until sparktiming. For example, an end of fuel injection timing may be shifted frombottom dead center (BDC) of the intake stroke to top dead center (TDC)of compression stroke. In this way, a higher amount of fuel may beinjected to the cylinder before spark, thereby allowing for an increasein fuel vaporization. After increasing the cranking speed and initiatingspark, for at least a first engine cycle after resuming spark, a fuelpulse-width may be adjusted based on the average vaporization time offuel (which governs the amount of fuel vaporized) during the previousnumber of non-firing engine cycles. In one example, the fuel pulse-widthmay be decreased on the first cycle where spark is resumed as the amountof fuel vaporized during the previous number of engine cycles increases.As such, if there is a higher amount of pre-vaporized fuel availablewhen spark is initiated, future fueling schedule may be adjusted todecrease the total amount of fuel injected during subsequent injectionevents. As an example, the vaporization time may be estimated based onengine speed and fuel alcohol content, and the start of injection andfuel pulse-width may be adjusted based on the vaporization time suchthat an optimal amount of fuel is vaporized for combustion.

As such, the engine cranking at the reduced cranking speed with enginefueling for the number of engine cycles with spark disabled is used toimprove alcohol fuel vaporization, which reduces the occurrence ofmisfire events. However, if misfire does occur, the engine cranking maybe further adjusted. Misfire events may be detected based on inputs froma crankshaft position (acceleration) sensor.

FIG. 6A shows a first statistical example 602 of first firing eventcombustion stability at a first cranking speed of 250 rpm. In thisexample, 26 simulated engine-starts at cold-start conditions using 250rpm as cranking speed is shown. The x-axis shows a counter for thenumber of engine (first firing event) starts for a given cylinder. They-axis shows an indicated mean effective pressure (IMEP) whichrepresents an average cylinder pressure at each engine start. Lower thanthreshold IMEP may result in combustion instability and engine misfires.A standard deviation of IMEP (IMEP_SD) was computed taking into accountthe IMEP during each of the 26 simulated engine-starts. IMEP_SD is anindicator of combustion stability and higher the value of the standarddeviation, the higher is the possibility of engine misfires. In thisexample, the IMEP_SD is 1.24 indicating a higher possibility of amisfire event.

FIG. 6B shows a second statistical example 604 of first firing eventcombustion stability at a second cranking speed of 200 rpm. In thisexample, 26 simulated engine-starts at cold-start conditions using 200rpm as cranking speed is shown. The x-axis shows a counter for thenumber of engine starts (first firing event) for a given cylinder andthe y-axis shows an indicated mean effective pressure (IMEP) at eachengine start. In this example, the indicator of combustion stability,IMEP_SD is 0.77. Compared to the example 602, the lower IMEP_SD inexample 604 shows that operating engine at a lower cranking speed duringcold-start improves combustion stability and decreases the possibilityof a misfire event.

FIG. 6C shows a second statistical example 606 of first firing eventcombustion stability at a third cranking speed of 150 rpm. Similar toexamples 602 and 604, in this example, 26 simulated engine-starts atcold-start conditions using 150 rpm as cranking speed is shown. Thex-axis shows a counter for the number of engine starts (first firingevent) for a given cylinder and the y-axis shows an indicated meaneffective pressure (IMEP) at each engine start. In this example 606, theindicator of combustion stability, IMEP_SD is 0.43 indicating a lowerpossibility of a misfire event compared to the IMEP_SD values as seen inexamples 602 and 604. In this way, by operating the engine at a lowercranking speed during cold-start conditions, combustion stability may beincreased and possibility of occurrence of misfire events may belowered. The improvement in combustion stability at lower crankingspeeds may be due to a longer time window for fuel vaporization beforecombustion. Also, by reducing the possibility of occurrence of misfireevents during cold-start conditions, unburned hydrocarbon emissions(UHC) relative to engine start at higher cranking speed may be reduced.In one example, for a given fuel alcohol content and air chargetemperature, during a cold-start condition, the controller may crank theengine via the starter motor at a cranking speed that is decreasedrelative to the nominal cranking speed with spark enabled and cylinderfueling enabled during an intake stroke. However, if the engineencounters misfiring events caused due to incomplete vaporization offuel, in subsequent engine starts with substantially similar fuelalcohol content and air charge temperature, such as subsequent enginestarts on the same drive cycle, the controller may crank the engine viathe starter motor at a cranking speed that is decreased relative to thenominal cranking speed with spark enabled and cylinder fueling extendedfrom the intake stroke into a compression stroke. If the combustionstability does not improve and misfire events still continue to occur,for subsequent engine starts with substantially similar fuel alcoholcontent and air charge temperature, in addition to cranking the engineat a lower speed and continuing fueling into the compression stroke, thecontroller may also disable spark for a number of engine cycles toincrease fuel vaporization before the first combustion event, therebyincreasing combustion stability.

At 220, the routine includes determining if engine cranking is complete.As such, once the engine reaches the idle speed, cranking via thestarter motor may no longer be required. If it is confirmed that theengine cranking is not completed, at 222, the starter motor may becontinued to be operated and the engine may be cranked at a speed lowerthan or equal to the nominal cranking speed. Also, during each cycle,fuel injection may be continued till spark. If it is determined that theengine cranking via the starter motor is completed, combustion may drivethe engine, and cranking may be stopped by suspending starter motoroperation.

If at 204, it is confirmed that cold-start conditions are not present,at 226, it may be inferred that the engine is started under hot-startconditions. Under hot-start, the engine temperature may be higher than athreshold temperature and the air charge temperature may be higher thanthe boiling point of the injected fuel. Therefore, prolongation ofvaporization time may not be desired during a hot-start. At 228, uponconfirmation of an engine hot-start, the controller may send a signal tothe starter motor to crank the engine at the nominal cranking speed.Also, fuel injection and spark may be enabled during engine cranking.Fuel may be injected into the cylinders starting from the TDC of theintake stroke to the BDC of the intake stroke, and spark may be enabledat TDC of the compression stroke.

In this way, during cold-starts, the engine may be cranked via thestarter motor at a lower cranking speed with fuel injection enabled andspark disabled for a first number of engine cycles, and then spark maybe enabled; and during a hot-start, the engine may be cranked via thestarter motor at a higher cranking speed with fuel injection and sparkenabled.

FIG. 3 shows an example plot 300 of change in air charge temperature andfuel boiling point with change in cranking speed. Spark may be set tooccur at the top dead center (TDC) at the end of the compression stroke.In this example, the x-axis is the time (in microseconds) to TDC (timeto spark) and the y-axis denotes temperature (in Kelvin). Plot 302 showschange in boiling point of a first fuel A over time when the enginecranking speed is 250 rpm. Plot 304 shows change in boiling point of thesame fuel A over time when the engine cranking speed is 150 rpm. In thedepicted example, 250 rpm may correspond to a nominal cranking speed and150 rpm may be a lower than nominal cranking speed during enginecold-start conditions. The boiling point of the fuel may be directlyproportional to the fuel alcohol content, the boiling point increasingas the fuel alcohol content increases. The alcohol content of the fuelmay be estimated via a sensor coupled to the fuel system. In oneexample, fuel A may be E10, E85, E100, etc. Plot 306 shows air chargetemperature during engine cranking at 250 rpm and plot 308 shows aircharge temperature during engine cranking at 150 rpm. Air chargetemperature may be estimated based on inputs from a manifold airtemperature sensor.

During cold-start conditions, air charge temperature may be lower thanfuel boiling point temperature. During the compression stroke, thecylinder pressure increases and there is a corresponding increase infuel boiling point and air charge temperature. When engine is beingcranked at 150 rpm, prior to time T1, the fuel boiling point is higherthan the air charge temperature. Point T1 corresponds to a time to TDCat which the air charge temperature increases to be equal to the boilingpoint of the fuel A. In the vaporization time window W1, between T1 andthe time to spark at BDC, the fuel boiling point continues to be higherthan the air charge temperature. Similarly, when the engine is beingcranked at 250 rpm, point T2 corresponds to a time (to TDC) at which theair charge temperature increases to be equal to the boiling point of thefuel A. In the vaporization time window W2 between T1 and the time tospark at BDC, the fuel boiling point continues to be higher than the aircharge temperature. Fuel may vaporize in the time windows W1 and W2during operation of the engine at 150 rpm and 250 rom respectively. Asseen from this example, since W1 is a longer time window compared to W2,an increased amount of fuel may vaporize (prior to spark) during engineoperation at a lower 150 rpm relative to engine operation at 250 rpm.Due to the higher amount of vaporized fuel, combustion stability may beimproved at lower cranking speeds.

FIG. 4 shows a map 400 of piston positions with respect to an engineposition, for a given engine cylinder, during engine cranking. The firstexample plot 402 shows piston positions with respect to an engineposition when gasoline is used as fuel during engine cranking athot-start conditions. The second example plot 404 shows piston positionswith respect to an engine position when gasoline is used as fuel duringengine cranking at cold-start conditions. The third example plot 406shows piston positions with respect to an engine position when E10 (10%Ethanol, 90% gasoline) is used as fuel during engine cranking atcold-start conditions. The fourth example plot 408 shows pistonpositions with respect to an engine position when E100 (100% Ethanol) isused as fuel during engine cranking at cold-start conditions.

Map 400 illustrates an engine position along the x-axis in crank angledegrees (CAD). Curves 403 (of plot 402), 405 (of plot 404), 407 (of plot406), and 409 (of plot 408) depict piston positions (along the y-axis),with reference to their location from top dead center (TDC) and/orbottom dead center (BDC), and further with reference to their locationwithin the four strokes (intake, compression, power and exhaust) of anengine cycle. As indicated by sinusoidal curves 403, 405, 407, and 409,a piston gradually moves downward from TDC, bottoming out at BDC by theend of the power stroke. The piston then returns to the top, at TDC, bythe end of the exhaust stroke. The piston then again moves back down,towards BDC, during the intake stroke, returning to its original topposition at TDC by the end of the compression stroke.

During hot-start conditions, the engine may be cranked at a nominalspeed. The curve 403 of the first example plot 402 shows the pistonpositions during engine operation at this nominal cranking speed. Fuelinjection may be carried out in the time window F1 between TDC and BDCof the intake stroke. Spark timing may be adjusted to correspond to theTDC at the end of the compression stroke. Due to the hot-startcondition, the air charge temperature may be higher than the boilingpoint of the fuel and an expected amount of fuel may vaporize beforespark. The boiling point of the fuel is based on the fuel ethanolcontent, the higher the percentage of alcohol, the higher is the boilingpoint. In the example plot 402, gasoline is used as fuel and the boilingpoint of gasoline (without any ethanol additive) is higher than that ofthe fuel blends comprising ethanol.

During cold-start conditions, the air charge temperature may be lowerthan the fuel boiling point until the compression stroke. The timewindow available for fuel vaporization (time period before spark whenair charge temperature is higher than fuel boiling point) may be smallerresulting in incomplete vaporization of fuel which may result incombustion instability. In order to increase the amount of fuelvaporization, the cranking speed may be lowered such that the durationof the compression stroke increases and the vaporization time windowincreases. The degree of cranking speed lowering may be based on theethanol content of the fuel. Also, during cold-start conditions, inorder to increase the total amount of fuel injected, fuel injection maybe extended from the intake stroke into the compression stroke (from TDCof intake stroke to TDC of compression stroke). In other words, fuelingmay be initiated in the intake stroke and continued until spark at TDCof compression stroke. The pulse-width of the fueling schedule may bemaintained at the same level as used during engine cranking underhot-start conditions. In this way, by continuing fueling at a constantrate until spark, a higher volume of fuel may be available forcombustion.

In the example plot 404, the curve 405 shows the piston positions duringengine cranking at cold-start conditions. Due to the cold-startcondition, the cranking speed may be reduced relative to the nominalspeed. In this example plot 404, gasoline is used as the fuel andfueling may be carried out in the time window F2, between the TDC of theintake stroke and the TDC of the compression stroke. The time window F2is longer than the time window F1. Therefore, by maintaining the samefueling pulse width during both conditions, a higher volume of fuel maybe injected before spark in the second example 404 compared to the firstexample 402. By increasing the amount of fuel injected and my extendingthe time window for vaporization, a higher volume of vaporized fuel maybe available for combustion.

In the example plot 406, the curve 407 shows the piston positions duringengine cranking at cold-start conditions when E10 is used as fuel. Dueto the higher ethanol content of E10 blend, the boiling point of thefuel may be higher than gasoline. Therefore to further increase the timewindow for fuel vaporization before spark, the cranking speed may befurther reduced relative to the nominal speed. Fueling may be carriedout in the time window F3, between the TDC of the intake stroke and theTDC of the compression stroke. The time window F3 is longer than each ofthe time windows F1 and F2. Therefore, by maintaining the same fuelingpulse width, a higher volume of fuel may be injected before spark in thethird example 406 compared to the first and second examples 402 and 404,respectively. An optimal level of E10 may vaporize in the extended timewindow created due to the lower cranking speed.

In the example plot 408, the curve 409 shows the piston positions duringengine cranking at cold-start conditions when E100 is used as fuel.Since this fuel is completely comprised of ethanol, its boiling pointmay be substantially higher than that of gasoline and E10. Therefore tofurther increase the time window for fuel vaporization before spark, thecranking speed may be further reduced relative to the cranking speedused for gasoline and E10 during cold-start. Fueling may be carried outin the time window F4, between the TDC of the intake stroke and the TDCof the compression stroke. The time window F4 is longer than each of thetime windows FI, F2, and F3. Therefore, by maintaining the same fuelingpulse width, a higher volume of fuel may be injected before spark in thefourth example 406 compared to the previous examples (plots 402, 404,and 406). The increased time window due to the lower cranking speedensures an optimal level of vaporization of the E100 fuel. In this way,during cold-start conditions, based on the ethanol content of the fuel,the cranking speed of the engine may be adjusted and fueling may beextended until spark to facilitate an optimal amount of fuelvaporization for stable combustion.

FIG. 5 shows an example engine start with adjusted cranking speed. Map500 depicts injection timing, spark timing, and cranking speed duringengine cranking. The first plot, line 502, shows engine cranking speedduring an engine hot-start when gasoline is used as fuel. The secondplot, line 504, shows engine cranking speed during an engine cold-startwhen gasoline is used as fuel. The third plot, line 506, shows enginecranking speed during an engine cold-start when E10 fuel blend (10%ethanol and 90% gasoline) is used. The fourth plot, line 508, showsengine cranking speed during an engine cold-start when E100 fuel (100%ethanol) is used. The x-axis denotes the engine cycle (number) afterengine start. In this example, four engine cycles are shown, each cyclecomprising an intake, a compression, a power, and an exhaust stroke.

During a hot-start condition (as shown by the first plot), thecontroller may send a signal to an actuator coupled to the starter motorto crank the engine at a nominal cranking speed S1. In the first plot,gasoline is used as fuel and L1 denotes an amount of gasoline injectedduring each engine cycle. In this plot, four engine cycles are shown,and in each cycle an equal amount of fuel may be injected during theintake stroke. Spark may be initiated at the end of the compressionstroke of each engine cycle, as denoted by S. The engine speed may bemaintained at the nominal speed during each engine cycle. The lack of an“S” label means that there is no spark event for that cycle.

During a cold-start condition, the controller may send a signal to anactuator coupled to the starter motor to crank the engine at a lowerthan nominal cranking speed S2. In the second plot, gasoline is used asfuel and L2 denotes an amount of gasoline injected during each enginecycle as engine is cranked at cold-start. Due to the lower crankingspeed, there is an increase in the time window available for fuelvaporization. In this plot, four engine cycles are shown, and in eachcycle an equal amount of fuel may be injected during each of the intakestroke and the compression stroke. By injecting fuel during both theintake stroke and the compression stroke and by lowering the crankingspeed, a higher volume of fuel may be injected and an increased amountof fuel may be vaporized. As such, fuel may be injected after bottomdead center (BDC) of the intake stroke of an engine cycle and afterintake valve closing such that heating of the intake charge has starteddue to compression, to top dead center of a compression stroke of eachengine cycle.

As seen in this example, the amount of gasoline injected duringcold-start, L2 is higher than the amount of gasoline injected duringhot-start, L1. In order to increase the amount of vaporized fuelavailable for combustion, spark may be disabled for a number of enginecycles. The number of non-firing engine cycles (without spark) may beselected based on the alcohol content of the injected fuel and theambient temperature so as to enable a larger portion of the fuel to bevaporized by the time spark is enabled. For gasoline as fuel (noethanol), spark may be disabled for one engine cycle and at the end ofthe compression stroke of the second cycle, spark may be initiated.Also, the cranking speed may be increased to the nominal cranking speedS1 at the end of the second engine cycle. By raising the cranking speedafter the number of engine cycles have elapsed, and resuming spark, theintake manifold pressure may be lowered and cylinder combustion can beperformed with a higher degree of fuel vaporized before combustion isinitiated.

In the third plot, E10 (10% ethanol and 90% gasoline) is used as fuelwhich has a higher boiling point than gasoline. Therefore the amount offuel injected and the vaporization time window before spark may beincreased to facilitate vaporization of an optimal amount of fuel. L3denotes an amount of E10 injected during both the intake and compressionstrokes of each engine cycle as engine is cranked at cold-start. Thecranking speed may be further decreased to speed S3 (S3 lower than eachof S2 and S1) to increase the time window available for fuelvaporization. As seen in this example, the amount of E10 injected duringcold-start, L3 is higher than the amount of gasoline injected duringcold-start, L2. In order to increase the amount of vaporized E10 fuelavailable for combustion, spark may be disabled for two engine cyclesand at the end of the compression stroke of the third cycle, spark maybe initiated. The cranking speed may be increased to the nominalcranking speed S1 at the end of the third engine cycle to lower theintake manifold pressure.

In the fourth plot, E100 (100% ethanol) is used as fuel which has ahigher boiling point than E10. Therefore the amount of fuel injected andthe vaporization time window before spark may be further increased tofacilitate vaporization of an optimal amount of fuel. L4 denotes anamount of E100 injected during both the intake and compression strokesof each engine cycle as engine is cranked at cold-start. The crankingspeed may be further decreased to speed S4 (S4 lower than S3) toincrease the vaporization time window. In order to further increase theamount of vaporized E100 fuel available for combustion, spark may bedisabled for three engine cycles and at the end of the compressionstroke of the fourth cycle, spark may be initiated. The cranking speedmay be increased to the nominal cranking speed S1 at the end of thethird engine cycle to lower the intake manifold pressure. In this way,by adjusting cranking speed and fueling amount based on ethanol contentin fuel, and by operating the engine without spark for a number ofcycles, a higher amount of fuel may be vaporized for optimal engineperformance at cold-start conditions.

In this way, by lowering cranking speed to below the nominal speed whilemaintaining spark deactivated for a number of engine cycles, a largertime window is provided for fuel vaporization. By increasing thevaporization time window, a higher amount of fuel may be vaporizedbefore spark is initiated, thereby increasing combustion stability andreducing feed gas hydrocarbon emissions. By increasing the crankingspeed after the number of engine cycles have elapsed, intake manifoldpressure may be increased, thereby further improving combustionstability. The technical effect of continuing fuel injection until sparkduring each engine cycle, a higher amount of fuel may be injectedresulting in an increase in the amount of vaporized fuel available forcombustion. By adjusting the cranking speed, fuel injection, and thenumber of non-firing cycles based on the ethanol content of the fuel, adesired amount of vaporized fuel may be available even for higheralcohol content fuels. Overall, by increasing the degree of fuelvaporization, engine performance, fuel economy and emissions quality maybe increased.

An example engine method comprises: for a number of engine cycles sincea first engine cycle of an engine cold-start, cranking the engine via astarter motor with cranking speed decreased relative to a nominalcranking speed while injecting fuel and disabling spark; and after thenumber of engine cycles with injected fuel compressed and expanded,increasing the cranking speed to the nominal cranking speed andinitiating spark. In any preceding example further, additionally oroptionally, the number of engine cycles is based on an alcohol contentof injected fuel, the number of engine cycles increased as the alcoholcontent of the injected fuel increases. In any or all of the precedingexamples, additionally or optionally, the number of engine cycles isfurther based on an air charge temperature at a time of engine start,the number of engine cycles increased as the air charge temperaturedecreases. In any or all of the preceding examples, additionally oroptionally, the decreased cranking speed is based on an alcohol contentof injected fuel, the cranking speed decreased further relative to thenominal speed as the alcohol content of the injected fuel increases. Anyor all of the preceding examples further comprises, additionally oroptionally, for the number of engine cycles, initiating fueling afterbottom dead center (BDC) of the intake stroke of an engine cycle andafter intake valve closing and terminating fueling at TDC of compressionstroke of the engine cycle. Any or all of the preceding examples furthercomprises, additionally or optionally, after increasing the crankingspeed and initiating spark, adjusting a fuel pulse-width based on anamount of fuel vaporized during the number of engine cycles. In any orall of the preceding examples, additionally or optionally, the fuelpulse-width is decreased as the amount of fuel vaporized during thenumber of engine cycles increases. In any or all of the precedingexamples, additionally or optionally, injecting fuel includes extendingan end of injection timing, the end of injection timing extended towardsa top dead center of compression stroke as the cranking speed isdecreased.

Another example method comprises: during a first engine start, crankingthe engine via a starter motor at a lower cranking speed with fuelinjection enabled and spark disabled for a first number of enginecycles, and then resuming spark; and during a second engine start,cranking the engine via the starter motor at a higher cranking speedwith fuel injection and spark enabled. In any of the preceding examples,additionally or optionally, the first engine start is a cold-start andthe second engine start is a hot-start. In any or all of the precedingexamples, additionally or optionally, an alcohol content of fuelinjected during the first engine start is higher than the alcoholcontent of fuel injected during the second engine start. In any or allof the preceding examples, additionally or optionally, the first numberof engine cycles is based on the alcohol content of the injected fuel,the first number of engine cycles increased as the alcohol contentincreases. In any or all of the preceding examples, additionally oroptionally, the first number of engine cycles is further based on chargeair temperature at the first engine start, the first number of enginecycles increased as the charge air temperature decreases. Any or all ofthe preceding examples further comprises, additionally or optionally,during the first engine start, after completion of the first number ofengine cycles, cranking the engine via the starter motor at the highercranking speed with fuel injection enabled and spark enabled, anddiscontinuing starter motor operation when engine idling speed isreached. Any or all of the preceding examples further comprises,additionally or optionally, during the first engine start, aftercompletion of the first number of engine cycles, cranking the engine viathe starter motor at the lower cranking speed with fuel injectionenabled and spark enabled, and discontinuing starter motor operationwhen engine idling speed is reached. In any or all of the precedingexamples, additionally or optionally, during the first engine start,fuel is injected after bottom dead center (BDC) of the intake stroke ofan engine cycle and after intake valve closing to the top dead center ofa compression stroke of each engine cycle for the first number of enginecycles, and wherein during the second engine start, fuel is injectedfrom top dead center of an intake stroke to the bottom dead center ofthe intake stroke of each engine cycle.

Yet another example method comprises: during a first engine cold-startof an alcohol-fueled engine, cranking the engine via a starter motor ata cranking speed that is decreased relative to a nominal cranking speedwith spark enabled and cylinder fueling during an intake stroke; duringa second engine cold-start of the alcohol-fueled engine, cranking theengine via the starter motor at the decreased cranking speed with sparkenabled and cylinder fueling extended from the intake stroke into acompression stroke; and during a third engine cold-start of thealcohol-fueled engine, cranking the engine via the starter motor at thedecreased cranking speed with spark disabled and injected fuelcompressed and expanded for a number of engine cycles, and theninitiating spark. In any of the preceding examples, additionally oroptionally, an alcohol content of fuel injected during the thirdcold-start is higher than the alcohol content of fuel injected duringthe second cold-start, and wherein the alcohol content of fuel injectedduring the second cold-start is higher than the alcohol content of fuelinjected during the first cold-start. In any or all of the precedingexamples, additionally or optionally, an air charge temperature duringthe third cold-start is lower than the air charge temperature during thesecond cold-start, and wherein the air charge temperature during thesecond cold-start is lower than the air charge temperature during thefirst cold-start. In any or all of the preceding examples, additionallyor optionally, during the first cold-start, fuel injection is started atTDC of the intake stroke and ended at BDC of the intake stroke, andwherein during each of the second and third cold-start, fuel injectionis started after bottom dead center (BDC) of the intake stroke of anengine cycle and after intake valve closing and ended at TDC of thecompression stroke.

In a further representation, an engine system comprises: a startermotor; an engine including an intake manifold, a plurality of cylinders,and an exhaust manifold; an exhaust temperature sensor coupled to theexhaust manifold; an air charge temperature sensor coupled to the intakemanifold; a crankshaft position sensor coupled to a crankshaft; a fuelsystem including one or more fuel injectors coupled to the plurality ofcylinders; an ignition system including one or more spark plugs coupledto the plurality of cylinders; and a controller with computer readableinstructions stored on non-transitory memory for: in response to anengine cold-start condition, actuating the starter motor to crank theengine at a lower than nominal cranking speed, actuating the fuelinjectors to inject fuel from a top dead center (TDC) of an intakestroke to TDC of a compression stroke, and deactivating spark for anumber of number of engine cycles after engine start; and aftercompletion of the number of engine cycles, actuating the starter motorto crank the engine at the nominal cranking speed, maintaining fuelingfrom TDC of the intake stroke to TDC of the compression stroke,actuating the spark plug to initiate spark at TDC of the compressionstroke until engine idling speed is reached. In any preceding example,additionally or optionally, the lower than nominal cranking speed andthe number of engine cycles is based on an alcohol content of the fuel,the cranking speed decreased with an increase in the alcohol content inthe fuel, and the number of engine cycles increased with an increase inthe alcohol content in the fuel. In any or all of the precedingexamples, additionally or optionally, the controller includes furtherinstructions for: in response to engine speed reaching the idling speed,deactivating the starter motor, and actuating the fuel injectors toinject fuel from TDC of the intake stroke to bottom dead center (BDC) ofthe intake stroke.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. An engine method, comprising: for a number of engine cycles since afirst engine cycle of an engine cold-start, cranking the engine via astarter motor, while injecting fuel and disabling spark, with crankingspeed decreased relative to a nominal cranking speed; and after thenumber of engine cycles with injected fuel compressed and expanded,increasing the cranking speed to the nominal cranking speed andinitiating spark.
 2. The method of claim 1, wherein the number of enginecycles is based on an alcohol content of injected fuel, the number ofengine cycles increased as the alcohol content of the injected fuelincreases, wherein each and every of the number of cycles occurs withoutany spark event therein.
 3. The method of claim 2, wherein the number ofengine cycles is further based on an air charge temperature at a time ofengine start, the number of engine cycles increased as the air chargetemperature decreases.
 4. The method of claim 1, wherein the decreasedcranking speed is based on an alcohol content of injected fuel, thecranking speed decreased further relative to the nominal speed as thealcohol content of the injected fuel increases.
 5. The method of claim1, further comprising, for the number of engine cycles, initiatingfueling after bottom dead center (BDC) of the intake stroke of an enginecycle and after intake valve closing, and terminating fueling at TDC ofcompression stroke of the engine cycle.
 6. The method of claim 1,further comprising, after increasing the cranking speed and initiatingspark, adjusting a fuel pulse-width based on an amount of fuel vaporizedduring the number of engine cycles.
 7. The method of claim 6, whereinthe fuel pulse-width is decreased as the amount of fuel vaporized duringthe number of engine cycles increases.
 8. The method of claim 1, whereininjecting fuel includes extending an end of injection timing, the end ofinjection timing extended towards a top dead center of compressionstroke as the cranking speed is decreased.
 9. An engine method,comprising: during a first engine start, cranking the engine via astarter motor at a lower cranking speed with fuel injection enabled andspark disabled for a first number of engine cycles, and then resumingspark; and during a second engine start, cranking the engine via thestarter motor at a higher cranking speed with fuel injection and sparkenabled.
 10. The method of claim 9, wherein the first engine start is acold-start and the second engine start is a hot-start.
 11. The method ofclaim 9, wherein an alcohol content of fuel injected during the firstengine start is higher than the alcohol content of fuel injected duringthe second engine start.
 12. The method of claim 11, wherein the firstnumber of engine cycles is based on the alcohol content of the injectedfuel, the first number of engine cycles increased as the alcohol contentincreases.
 13. The method of claim 9, wherein the first number of enginecycles is further based on charge air temperature at the first enginestart, the first number of engine cycles increased as the charge airtemperature decreases.
 14. The method of claim 9, further comprising,during the first engine start, after completion of the first number ofengine cycles, cranking the engine via the starter motor at the highercranking speed with fuel injection enabled and spark enabled, anddiscontinuing starter motor operation when engine idling speed isreached.
 15. The method of claim 9, further comprising, during the firstengine start, after completion of the first number of engine cycles,cranking the engine via the starter motor at the lower cranking speedwith fuel injection enabled and spark enabled, and discontinuing startermotor operation when engine idling speed is reached.
 16. The method ofclaim 9, wherein during the first engine start, fuel is injected afterbottom dead center (BDC) of the intake stroke of an engine cycle andafter intake valve closing, to top dead center of a compression strokeof each engine cycle for the first number of engine cycles, and whereinduring the second engine start, fuel is injected from top dead center ofan intake stroke to bottom dead center of the intake stroke of eachengine cycle.
 17. A method for an engine, comprising: during a firstengine cold-start of an alcohol-fueled engine, cranking the engine via astarter motor at a cranking speed that is decreased relative to anominal cranking speed with spark enabled and cylinder fueling during anintake stroke; during a second engine cold-start of the alcohol-fueledengine, cranking the engine via the starter motor at the decreasedcranking speed with spark enabled and cylinder fueling extended from theintake stroke into a compression stroke; and during a third enginecold-start of the alcohol-fueled engine, cranking the engine via thestarter motor at the decreased cranking speed with spark disabled andinjected fuel compressed and expanded for a number of engine cycles, andthen initiating spark.
 18. The method of claim 17, wherein an alcoholcontent of fuel injected during the third cold-start is higher than thealcohol content of fuel injected during the second cold-start, andwherein the alcohol content of fuel injected during the secondcold-start is higher than the alcohol content of fuel injected duringthe first cold-start.
 19. The method of claim 17, wherein an air chargetemperature during the third cold-start is lower than the air chargetemperature during the second cold-start, and wherein the air chargetemperature during the second cold-start is lower than the air chargetemperature during the first cold-start.
 20. The method of claim 17,wherein during the first cold-start, fuel injection is started at TDC ofthe intake stroke and ended at BDC of the intake stroke, and whereinduring each of the second and third cold-start, fuel injection isstarted after bottom dead center (BDC) of the intake stroke of an enginecycle and after intake valve closing and ended at TDC of the compressionstroke.